There is known an electronic device wherein various electronic components such as a semiconductor element, a heat-generating element, and a Peltier element, are mounted on a circuit substrate including a metal layer on a base formed of ceramics. An electronic component mounted on such a circuit substrate generates heat when operating. Because of an increased integration of electronic components and a reduction in size and thickness of electronic devices in recent years, an amount of heat applied to a volume of a circuit substrate is increasing, and therefore, in addition to a demand for there to be no separation at a junction between the base formed of ceramics and the metal layer, there is a demand for a circuit substrate with high heat dissipation.
Because of this demand, using a base including a through hole, improvement of heat dissipation is carried out utilizing a conductor provided across the metal layer inside the through hole. For example, a non-shrinking metal paste including a conductive powder which contains a metal powder as a main component, an expanding agent, and a vehicle is proposed in Patent Literature 1 as a metal paste which forms a through conductor.